Growing up on a dead-end street in suburbia, Tatyana and Hannah McFadden raced their wheelchairs up, down and all around. Their family challenged cul-de-sac convention, but also fit right in.

Two moms, three children, a grandma and two dogs. A basketball hoop in the driveway. Purple wheelchairs scattered throughout the garage. Sports equipment, and prosthetic legs, stuffed in cramped closets.

“It’s been just such an amazing year,” Debbie McFadden said, standing alongside her daughters on the backyard patio. Dozens of camera phones clicked.

The buttercream on the sheet cake told the rest of the story: “Tatyana & Hannah Go for the Gold!” was written in red script across the icing, and two tiny wheelchairs raced on a fondant track.

The daughters were raised to believe they could do anything, no matter what the physical impairment, and this is what their uncommon determination has wrought: At the Paralympic Games, which begin Wednesday in Rio de Janeiro, Tatyana McFadden could become the first athlete to sweep every distance in wheelchair racing. She will compete in the 100 meters and the marathon — and everything in between. She could leave Rio with seven gold medals.

Her sister Hannah is racing in three of the same events, including the 4×100 relay. If the McFaddens finish side-by-side on the podium, they will be the first sisters to do so in a Paralympics.

The odds of this? Longer than a marathon, especially given their start. “You know, when Tatyana and Hannah came here, Tatyana was told by doctors at Johns Hopkins she probably wouldn’t live long, and they said Hannah would never be active,” Debbie McFadden told the gathering at their Rio send-off party.

One of the best athletes most Americans have never heard of, Tatyana McFadden may be hard to miss in the coming months. Her Phelpsian medal quest will be a focal point for NBC’s Paralympics coverage — more than 70 hours across NBC’s networks and sports app, compared with six hours of coverage for the London Paralympics four years ago.

“In the U.S., you don’t know about the Paralympics,” said Philip Craven, the president of the International Paralympic Committee. “You’re going to get to know. Give your people a chance to get to know Tatyana. It will take their minds off the presidential election.”

McFadden’s image appears on more than a million Coke cans. Her orphanage-to-ESPY life story will be told, and retold, in commercials. In the time leading up to Rio, BP became the first United States Olympic Committee corporate partner to sponsor more Paralympians than Olympians.

Now that Michael Phelps has packed up his Speedo and gone home and Simone Biles has clapped her last cloud of chalk into the rafters, will the American public stay for the Paralympics after-party?

“We’re on the cusp of breaking the barriers for Paralympic sport,” Tatyana McFadden said. “It’s taken a lot of hard work and dedication, trying to teach society what it means to be a Paralympian, that we’re not any different, that we’re just like the Olympians, with the same training sites, sponsorships, medals and venues.”

If not the same rewards.

The United States Olympic Committee awards $25,000 to every American who wins an Olympic gold versus $5,000 for every Paralympic gold; $15,000 for Olympic silver versus $3,500 for Paralympic silver; and $10,000 for Olympic bronze versus $2,500 for Paralympic bronze.

“If you don’t speak out, it’s going to stay the same,” she said. “Because I’ve been in the sport for a bit, I can be an educator. I want to give back for the next generations to come, however long I’ll be racing. I think it’s really, really important to have that voice.”

A ‘Unique Household’

Born with spina bifida and adopted from a Russian orphanage, Tatyana McFadden, 27, is paralyzed from the waist down. Hannah McFadden, 20, adopted from Albania, born without a femur in her left leg, is an above-the-knee amputee. She uses a prosthesis to walk and a wheelchair to race.

Ruthi McFadden, 17, also adopted from Albania, is the outlier — no wheelchair, no prosthetic leg to pop off at airport security and hand to a T.S.A. agent, as Hannah does for kicks. She has no desire to run the length of a basketball court, let alone a marathon. “I don’t like to sweat,” she tells her sisters.

“Our family is a very unique household,” said Hannah McFadden, legs slung over an ottoman in the living room. “If you took a family photo right now, you got Grandma with an oxygen tank, probably sassing the photographer.” (The oxygen tank comes courtesy of decades of smoking; the sassing comes naturally.)

She continued: “Ruthi talking about all the boyfriends she has. Tatyana wishing she had all the boyfriends. And me saying, ‘Where’s the food?’ You’d have all those different things going on and oh, yeah, and then parents, Deb and Bridget. We have two moms.

“That was just the way it was. Having two moms wasn’t what really stood out about this family,” she said, in the deadpan of a mockumentary.

Earlier this year, after People magazine published a feature article with the headline, “Meet My Two Moms: Wheelchair Racing Sensation Tatyana McFadden Reveals How She Was Saved From a Bleak Russian Orphanage,” the family collectively chuckled.

It was not exactly breaking news. Debbie McFadden and Bridget O’Shaughnessey have been partners for 32 years. They kept their relationship and their shared parenting role low-key because they did not want headlines to read, “Raised by Two Moms, McFadden Wins Gold.”

“I’ve been public about it,” Tatyana McFadden said, “but I haven’t been always, ‘Oh, these are my two moms, these are my two moms, these are my two moms.’

“It’s something I grew up with, and it’s not any different to me. Our parents have been together, what, more than 30 years? They’re a great example of what love and relationships look like.”

They met when Debbie McFadden was still recovering from the effects of Guillain-Barré syndrome, a rare autoimmune disease. While she was in graduate school, the condition left her paralyzed from the neck down. As a result, she relied on an electric wheelchair for four years and then crutches for eight.

The obstacles Debbie McFadden faced while disabled — limited job and educational opportunities, snap judgments based on physical appearance — came to define her life’s work, as an advocate and a mother. “This can never be,” she told herself.

She became the United States commissioner of disabilities in 1989, appointed by President George H. W. Bush.

“Why, sir, this job?” she recalled asking the president.

“Because you’re a pain in the ass,” he replied. “I’d rather have you working for me than against me.”

(Bush, 92, did not recall the specific interaction, but spoke highly of McFadden, a spokesman, Jim McGrath, said.)

McFadden helped write the Americans With Disabilities Act of 1990, the milestone legislation that prohibits discrimination based on disability.

“She makes the impossible happen,” Hannah said. “That woman does not know the word ‘no.’” Debbie McFadden now serves as her daughters’ manager, or “momager,” as they call it.

O’Shaughnessey, who works in information technology for the United States Department of Health and Human Services, is the behind-the-scenes parent, the one fixing wheelchairs and wearing a headlamp for late-night wheelchair workouts on the track. She is the steady pace runner, the quiet complement to her force-of-nature partner.

On a stage in Times Square this summer, surrounded by Olympians and Paralympians, Tatyana McFadden described her early years in St. Petersburg, Russia.

“For the first six years in the orphanage, I received no medical treatment, so no wheelchair available,” she said, addressing the crowd at a news media event. “And I taught myself how to walk on my arms, using my arms as my legs to get around the orphanage.” The next speaker, Michelle Obama, waited in the wings.

“The sixth year changed my life for the better, when a woman happened to walk through the door, and that’s my mom Deborah McFadden. She’s here today.” She paused for applause and then continued.

Tatyana McFadden said sports had changed her life, and had perhaps saved it. Given her weak physical state at the time of her adoption, her parents signed her up for every sport they could find to build her strength.

“See that wooden fence?” Debbie McFadden said as she pulled into the parking lot outside the home of the Bennett Blazers, an adaptive sports program. “That’s where she was when we first put her in the racing chair and said, ‘Go.’”

A Lawsuit and a Legacy

Inside the gym, Tatyana’s legacy is everywhere — in her trademark candy purple racing chairs, still used by the current Blazers, and the imprint she has made on the children there today. She is their Stephen Curry, their Serena Williams, their autographed poster on a bedroom wall.

“Tatyana brings pride and recognition,” said David Elbert, whose daughter, Ruby, is part of the Blazers program. “She makes these kids stand up taller sometimes. Last Paralympics, Tatyana was on the gas pump. You pulled into BP, and Ruby was like, ‘Whoa.’”

In seventh grade, Ruby broke down Tatyana McFadden’s lawsuit against the Howard County school district for a social studies assignment.

When McFadden was 15, Ruby’s age now, she was the youngest member of the 2004 United States Paralympics team. After winning her first two Paralympic medals in Athens, she started her freshman year at Atholton High School in Columbia, Md. She had never imagined that earning a varsity letter would be the greater challenge.

Competing against able-bodied runners, McFadden did not expect her results to count; she just wanted to experience competitive sports. Citing safety concerns, school officials prohibited McFadden, a freshman, from racing alongside her high school track team. In 2005, the McFaddens filed suit, claiming no damages, against the Howard County Public School System. Until the case could be heard in federal court, the school allowed Tatyana to race separately, to circle an otherwise empty track after everyone else had run.

The highly publicized legal battle took a toll on the teenager. At times, she was booed on the track, ostracized by teammates and ripped on message boards. A teammate, the coach’s daughter, sent a scathing letter to local newspapers.

“I will no longer sit back and watch runners be treated unfairly because they are NOT disabled,” the 2007 letter said, according to The Washington Post. “Politically correct or not, I have been waiting several months to get all this off my chest.”

During the years of the lawsuit, McFadden turned to her grandmother Jo for support. “I’d be coming home being emotional and Grandma Jo would help me through it,” Tatyana said. “She reminds me that it’s about the long run.”

“It was a tough time for her,” Grandma Jo said. “A lot of tears.”

Grandma Jo, O’Shaughnessey’s mother, moved in with the family when the children were young. She was the one home when Mom (Debbie McFadden) traveled abroad, running an international adoption agency after her term as commissioner of disabilities. And Grandma Jo was the one home when Mama (Bridget O’Shaughnessey) was still at work in Washington.

McFadden eventually won the right to race with her classmates — and the suit paved the way for the passage of a state law that guaranteed all students with disabilities the right to participate in sports. Then it became a national mandate. Three years ago, the United States Department of Education’s Office of Civil Rights issued a letter of guidance clarifying school districts’ legal obligation to provide equal access to extracurricular activities to all students.

The long run — the marathon view, if you will — made the struggle worth it. It made life easier for those who followed, including Hannah, who did not have to deal with the obstacles or animosity her sister had faced.

In Tatyana McFadden’s book for young readers, “Ya Sama! Moments From My Life,” published this year, there is a chapter about the case, with the ugly moments softened or omitted. “I didn’t want to make it so dark or so tragic,” she said.

The Russian phrase “Ya sama!” can be translated as “I can do it” or “I can do it myself.” It is a phrase she learned as a young child in her St. Petersburg orphanage and one she uses now when faced with a challenge.

“Any race that Tatyana is on the starting line is a race she can win,” said Adam Bleakney, her coach for the Paralympics and at the University of Illinois, where she is a graduate student. “So I wouldn’t be surprised if she wins seven golds. One of her strengths is her ability to have a very singular focus, whatever the task at hand. There is never a reservation or doubt when she has a goal in her mind. Most of us will get a sliver of doubt, but I don’t think that ever happens to Tatyana.”

After returning with three golds from the 2012 Summer Paralympic Games in London, Tatyana tried skiing for the first time. She made the 2014 Winter Paralympics team and left Sochi with a silver medal, her 11th over all.

In Rio, McFadden is likely to win gold several times over, as she is the world-record holder in the 100, 400, 800, 1,500 and 5,000 meters.

The United States relay team — nicknamed the McRelay, with a lineup of the McFadden sisters, Amanda McGrory and Chelsea McClammer — is a gold medal contender. And Tatyana McFadden is favored to win the marathon, after having swept the Boston, London, Chicago and New York marathons for the last three years.

In April, at the London Marathon, McFadden raced wheel to wheel and shoulder to shoulder with her Swiss rival Manuela Schär. McFadden’s arms throbbed as she pushed past Buckingham Palace, unable to shake Schär, who had saved energy for the final push by riding in McFadden’s draft. The duo headed for the finish at the Mall. As Schär tried to outkick her rival, McFadden floored it to the finish, winning by a second.

As her parents watched, even they were astounded. Where did that sprint come from? they asked her.